Although photochemistry‐enabled escape of oxygen is a dominant atmospheric loss process at Mars today, ion outflow plays an essential role in the long‐term evolution of Mars' atmosphere. Apart from heavy planetary ions such as O + , O 2 + , and CO 2 + , the loss of planetary protons is also important because it could be related to water loss. To study planetary proton loss due to solar wind interaction, we improve the 4‐species (O + , O 2 + , CO 2 + , and H + ) single‐fluid magnetohydrodynamic (MHD) model of Mars, to a 5‐species (separating planetary protons and solar wind protons) MHD model so that the two types of protons can be tracked separately. The global distributions of solar wind protons and planetary ions at low altitudes are investigated. The calculated planetary proton escape rates are larger than heavy ion loss rates and solar wind proton inflows for both solar maximum and minimum conditions. Planetary proton escape rates are 1–2 orders less than neutral hydrogen loss, suggesting that planetary protons could contribute to no >10% of the hydrogen loss under current conditions. By comparing normal cases with cases for which H‐O charge exchange reactions or electron impact ionizations are switched off, we find that H‐O charge exchange mainly affects densities at low altitudes, while impact ionizations exert great influence on escape rates at high altitudes. The overall results suggest the specific treatment of proton origins in models of Mars atmosphere escape provides better insight into the contributing processes, and should be included in future studies focusing on water's fate.

The succinct title of this book belies a great breadth of discussion and detail regarding not only ionospheres themselves but all those physical and chemical processes upon which their characteristics, dynamics and energetics depend. After a descriptive scene-setting first two chapters introducing solar system neutral and ionised atmospheres, it moves rapidly and comprehensively into the mathematics of the underlying mechanisms such as plasma distribution functions, collisional processes, 13-moment transport equations, diffusion and shocks. This requires the reader to have good graduate-level agility in mathematics and, although it is written in a logical and lucid fashion, this may deter readers with less experience. Conversely, it will be welcome reference material for those whose work is in plasma and space physics and for whom such material is essential and yet difficult to come by in a single publication. There follows, amongst many other things, an extensive discussion of influences. Such is the authors' determination to provide a complete toolkit for understanding how ionospheres are formed, their energy sources and sinks and their coupling to the planetary atmosphere, that the first real mention of the layers of the Earth's ionosphere does not appear until over half-way through the book. It does not dwell on the Earth's ionosphere for a disproportionate time, however, but treats it with commensurate weight to the ionospheres of the other planets, of their satellites and of comets. Therefore, this is not, in my view, a book for those who are looking for a comprehensive treatise on the Earth's ionosphere and its phenomenology; there are several of those already in print. Instead, this publication stands apart as taking a generic look at ionospheres from first principles. In addition, whereas others often look at the Earth's ionosphere from a geocentric perspective, this work takes a more global view as if looking on the system from outside the planet. It should prove excellent both as a tutorial for postgraduate or specialist final-year students and as a reference book for atmospheric scientists and plasma physicists. Its value for students is greatly enhanced by the problems set at the end of most chapters and by its extensive appendices which provide fundamental mathematical equations and model parameters, etc. The set problems, however, are predominantly numerical or formulaic derivations and are excluded from the more descriptive chapters (e.g. Space Environment, Measurement Techniques); therefore the student appears to be asked to test their mathematical ability more than their philosophical understanding. On the other hand, many of the mathematical problems would suit plasma physics students with little direct interest in ionospheres. The final chapter on ionospheric measurement techniques seems a little superfluous and patchy but the general references supplied should be able to satiate whetted appetites. Ionospheres is a book which I anticipate will appear as a standard on bookshelves both in research laboratories and university libraries. The combined sixty-five years of experience of the two authors at the cutting-edge of this topic area should certainly provide a sound and reliable knowledge-base for dedicated students and academics alike. Dr M J Jarvis Geospace-Atmosphere Transfer Functions, British Antartic Survey, Madingly Road, Cambridge CB3 0ET

We study the effect of negatively charged dust on the magnetic-field-aligned polarisation electrostatic field ($\boldsymbol {E}_{\parallel }$) using Cassini's RPWS/LP in situ measurements during the ‘ring-grazing’ orbits. We derive a general expression for $\boldsymbol {E}_{\parallel }$ and estimate for the first time in situ $\lVert \boldsymbol {E}_{\parallel } \rVert$ (approximately $10^{-5} \, \text {V}\, \text {m}^{-1}$) near the Janus and Epimetheus rings. We further demonstrate that the presence of the negatively charged dust close to the ring plane ($\vert \text {Z} \vert \lesssim 0.11 \, \text {R}_{s}$) amplifies $\lVert \boldsymbol {E}_{\parallel } \rVert$ by at least one order of magnitude and reverses its direction due to the effect of the charged dust gravitational and inertial forces. Such reversal confines the electrons at the magnetic equator within the dusty region, around $0.047 \, \text {R}_{s}$ above the ring plane. Furthermore, we discuss the role of the collision terms, in particular the ion–dust drag force, in amplifying $\boldsymbol {E}_{\parallel }$. These results imply that the charged dust, as small as nanometres in size, can have a significant influence on the plasma transport, in particular ambipolar diffusion along the magnetic field lines, and so their presence must be taken into account when studying such dynamical processes.

The primary objective of this research program is to improve our understanding of the physical processes occurring in the interaction of the solar wind with Venus. This will be accomplished through the use of numerical solutions of the two- and three-dimensional magnetohydrodynamic (MHD) equations and through comparisons of the computed results with available observations. A large portion of this effort involves the study of processes due to the presence of the magnetic field and the effects of mass loading. Published papers are included in the appendix.

An abstract is not available for this content. As you have access to this content, full HTML content is provided on this page. A PDF of this content is also available in through the 'Save PDF' action button.

An appreciation of how large‐scale magnetic fields can be maintained in the subsolar Venus ionosphere by the solar wind interaction was previously obtained with one‐dimensional diffusion/convection numerical models. Here, the solution of the diffusion/convection or dynamo equation for the ionospheric field is generalized to three dimensions under the assumption that the field and flow at the upper boundary (in the magnetic barrier) is known from a previous gas dynamic model, and that the ionospheric plasma velocity is known. The latter is given by the combination of the antisunward convection inferred from measurements, and the downward drift calculated from the observed vertical thermal pressure gradient. The results suggest that the low‐altitude magnetosheath field draping may be distorted by the interaction with the ionosphere in such a manner that there is an apparent "focusing" of the field toward the subsolar point. Although the model resolution is too course to resolve the magnetic "belt," an ionospheric field is produced that is strongest and parallel to the overlying field in the subsolar region, as is observed.

The Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission was launched on 5 May 2018 and successfully landed at Elysium Planitia (4.5oN, 135.9oE)on Mars on 26 November 2018. The InSight Lander carries a magnetometer to measure disturbances from the Martian ionosphere. In order to understand the daily variations in the magnet field measurements on Martian surface, in this study, we use the time-dependent MHD model to study how plasma conditions vary with local time above insight landing site using solar wind condition from MAVEN observation. Significant diurnal variations can be seen in all plasma quantities due to solar wind interactions and planetary rotation. The induced magnetic field is mainly in the same direction as the upstream IMF. However, it seems that the variations seen by the Insight magnetometer cannot be only due to the interaction of the solar wind. We also add a neutral wind effect in our simulations to further investigate possible causes of surface field changes.

This is a description of my 60‐year career in space science. I was lucky that my career started pretty much with the beginning of the space science era, when most measurements presented something new, exciting, and unexpected. It was also a time when there were plenty of opportunities and finding support was relatively easy.

Between 26 April and 15 September 2017, Cassini executed 23 highly inclined Grand Finale orbits through a new frontier for space exploration, the narrow region between Saturn and the D Ring, providing the first opportunity for obtaining in situ ionospheric measurements. During the Grand Finale orbits, the Radio and Plasma Wave Science instrument observed broadband whistler mode emissions and narrowband upper hybrid frequency emissions. Using known wave propagation characteristics of these two plasma wave modes, the electron density is derived over a broad range of ionospheric latitudes and altitudes. A two-part exponential scale height model is fitted to the electron density measurements. The model yields a double-layered ionosphere with plasma scale heights of 545/575 km for the northern/southern hemispheres below 4,500 km and plasma scale heights of 4,780/2,360 km for the northern/southern hemispheres above 4,500 km. The interpretation of these layers involves the interaction between the rings and the ionosphere. Plain Language Summary For the final 5 months of the Cassini mission in 2017, the spacecraft executed 23 orbits through a new frontier for space exploration, the narrow region between Saturn and the innermost of Saturn's main rings, the D Ring. For the first time in the history of space exploration, the Cassini instruments were able to take measurements inside Saturn's ionosphere. This paper provides the density distribution of Saturn's ionospheric electrons, derived from plasma waves detected by the Radio and Plasma Wave Science instrument. The electron density distributions with altitude and latitude show that the ionospheric electron densities peak at 10,000 particles per cubic centimeter at low altitudes in the equatorial region and drop below 100 particles per cubic centimeter at higher altitudes and latitudes. Two simple ionospheric scale height density models for the northern and southern hemispheres are presented.

This chapter summarizes our current understanding of the ionosphere of Saturn. We give an overview of Saturn ionospheric science from the Voyager era to the present, with a focus on the wealth of new data and discoveries enabled by Cassini, including a massive increase in the number of electron density altitude profiles. We discuss recent ground-based detection of the effect of ring rain on Saturn's ionosphere, and present possible model interpretations of the observations. Finally, we outline current model-data discrepancies and indicate how future observations can help in advancing our understanding of the various controlling physical and chemical processes.

The multifluid (MF) magnetohydrodynamic model of Mars is improved by solving an additional electron pressure equation. Through the electron pressure equation, the electron temperature is calculated based on the effects from various electron‐related heating and cooling processes (e.g., photoelectron heating, electron‐neutral collision, and electron‐ion collision), and thus, the improved model can calculate the electron temperature and the electron pressure force terms self‐consistently. Model results of a typical case using the MF with electron pressure equation included model are compared in detail to identical cases using the MF and multispecies models to identify the effect of the improved physics. We find that when the electron pressure equation is included, the general interaction patterns are similar to those with no electron pressure equation. However, the MF with electron pressure equation included model predicts that the electron temperature is much larger than the ion temperature in the ionosphere, consistent with both Viking and Mars Atmosphere and Volatile EvolutioN (MAVEN) observations. Using our numerical model, we also examined in detail the relative importance of different forces in the plasma interaction region. All three models are also applied to a MAVEN event study using identical input conditions; overall, the improved model matches best with MAVEN observations. All of the simulation cases are examined in terms of the total ion loss, and the results show that the inclusion of the electron pressure equation increases the escape rates by 50–110% in total mass, depending on solar condition and strong crustal field orientation, clearly demonstrating the importance of the ambipolar electric field in facilitating ion escape.

We present the electron density ( n e ) altitude profiles of Saturn's ionosphere at near‐equatorial latitudes from all 23 orbits of Cassini's Grand Finale. The data are collected by the Langmuir probe part of the Radio and Plasma Wave Science investigation. A high degree of variability in the electron density profiles is observed. However, organizing them by consecutive altitude ranges revealed clear differences between the southern and northern hemispheres. The n e profiles are shown to be more variable and connected to the D‐ring below 5,000 km in the southern hemisphere compared to the northern hemisphere. This observed variability is explained to be a consequence of an electrodynamic interaction with the D‐ring. Moreover, a density altitude profile is constructed for the northern hemisphere indicating the presence of three different ionospheric layers. Similar properties were observed during Cassini's final plunge, where the main ionospheric peak is crossed at ∼1,550‐km altitude.

The Pioneer and Voyager spacecraft made close-up measurements of Saturn's ionosphere and upper atmosphere in the 1970s and 1980s that suggested a chemical interaction between the rings and atmosphere. Exploring this interaction provides information on ring composition and the influence on Saturn's atmosphere from infalling material. The Cassini Ion Neutral Mass Spectrometer sampled in situ the region between the D ring and Saturn during the spacecraft's Grand Finale phase. We used these measurements to characterize the atmospheric structure and material influx from the rings. The atmospheric He/H2 ratio is 10 to 16%. Volatile compounds from the rings (methane; carbon monoxide and/or molecular nitrogen), as well as larger organic-bearing grains, are flowing inward at a rate of 4800 to 45,000 kilograms per second.

We study roles of the thermosphere and exosphere on the Martian ionospheric structure and ion escape rates in the process of the solar wind-Mars interaction. We employ a four-species multifluid magnetohydrodynamic model to simulate the Martian ionosphere and magnetosphere. The cold thermosphere background is taken from the Mars Global Ionosphere Thermosphere Model, and the hot oxygen exosphere is adopted from the Mars exosphere Monte Carlo model-Adaptive Mesh Particle Simulator. A total of four cases with the combination of 1-D (globally averaged) and 3-D thermospheres and exospheres are studied. The ion escape rates calculated by adopting 1-D and 3-D atmospheres are similar; however, the latter are required to adequately reproduce the ionospheric observations by the Mars Atmosphere and Volatile EvolutioN mission. In addition, our simulations show that the 3-D hot oxygen corona plays an important role in preventing planetary molecular ions (O-2(+) and CO2+) escaping from Mars, mainly resulting from the mass loading of the high-altitude exospheric O+ ions. The cold thermospheric oxygen atom, however, is demonstrated to be the primary neutral source for O+ ion escape during the relatively weak solar cycle 24.

We present new models of Saturn's equatorial ionosphere based on the first in situ measurements of its upper atmosphere. The neutral spectrum measured by Cassini's Ion and Neutral Mass Spectrometer, which includes substantial methane, ammonia, and organics in addition to the anticipated molecular hydrogen, helium, and water, serves as input for unexpectedly complex ionospheric chemistry. Heavy molecular ions are found to dominate Saturn's equatorial low-altitude ionosphere, with a mean ion mass of 11Da. Key molecular ions include H3O+ and HCO+; other abundant heavy ions depend upon the makeup of the mass 28 neutral species, which cannot be uniquely determined. Ion and Neutral Mass Spectrometer neutral species lead to generally good agreement between modeled and observed plasma densities, though poor reproduction of measured H+ and H-3(+) variability and an overabundance of modeled H-3(+) potentially hint at missing physical processes in the model, including a loss process that affects H-3(+) but not H+. Plain Language Summary Cassini's Grand Finale enabled the first-ever direct measurements of Saturn's upper atmosphere. Here we use Cassini's unique measurements to construct new models of the plasma in this important boundary region that separates the dense lower atmosphere from space. Based on the complex array of observed gases, we find that heavy molecular ions are dominant near Saturn's equator. This surprising result demonstrates that the chemistry in Saturn's equatorial upper atmosphere is substantially more complex than anticipated. The presence of these unexpected ions potentially represents a new method of monitoring Saturn's ionosphere remotely. Furthermore, as other Cassini measurements indicate that the complex chemistry is likely driven by an influx of ring-derived material, such observations may even help to track the evolution of Saturn's rings as they lose mass to its atmosphere.

Observations of the Mars upper atmosphere made from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft have been used to determine the loss rates of gas from the upper atmosphere to space for a complete Mars year (16 Nov 2014 - 3 Oct 2016). Loss rates for H and O are sufficient to remove similar to 2-3 kg/s to space. By itself, this loss would be significant over the history of the planet. In addition, loss rates would have been greater early in history due to the enhanced solar EUV and more-active Sun. Integrated loss, based on current processes whose escape rates in the past are adjusted according to expected solar evolution, would have been as much as 0.8 bar CO2 or 23 m global equivalent layer of H2O; these losses are likely to be lower limits due to the nature of the extrapolation of loss rates to the earliest times. Combined with the lack of surface or subsurface reservoirs for CO2 that could hold remnants of an early, thick atmosphere, these results suggest that loss of gas to space has been the dominant process responsible for changing the climate of Mars from an early, warmer environment to the cold, dry one that we see today.